Dazai was sent out on a mission for the ADA, it was a specific undercover mission to collect information. The task was simple, he just had to dance with a few women, charm a few other men, get the info he needed and leave.

Really simple.

So, is it really his fault that he had a little more to drink?

So, is it really his fault if he fucked up, and is currently dancing with you in his arms after stealing you from your date?

Well…